1. Field of the Invention
The present invention relates to a focus detection apparatus and focus detection method for use in an image capturing apparatus such as a camera.
2. Description of the Related Art
Conventionally, a phase-difference detection method is commonly known as a focus detection method for use in an automatic focus detection apparatus of a camera. The phase-difference detection method refers to a method of forming, onto a pair of line sensors, an image of light fluxes from an object, which have passed through different exit pupil regions of an imaging lens, and obtaining the phase difference between a pair of electrical signals of an image of the object, obtained by photoelectric conversion, thereby detecting the defocus amount of the imaging lens.
In addition, a technique for a multipoint focus detection apparatus is also disclosed, in which a line sensor is divided into a plurality of blocks to control signal charge accumulation for each block, and the detection of the defocus amount is carried out from a plurality of images of an object corresponding to the positions of the respective blocks (for example, see Japanese Patent Laid-Open No. 2003-215442).
However, in the focus detection apparatus described in Japanese Patent Laid-Open No. 2003-215442, each block has a short range of field. The shorter range of field may result in the inability to capture the contrast of an object sufficiently, thus leading to a problem of reduction in focus detection accuracy. In addition, the shorter range of field limits the detectable defocus range, thus causing the problem of inability to control focus detection for a significantly defocused image of an object.